San Francisco: Refuting the claims of Federal Bureau of Investigation (FBI) in the aftermath of Texas church shooting, Apple reportedly said it offered to help the investigating agency in opening the attacker's encrypted iPhone.

The Cupertino-based giant said it reached out to the bureau "immediately" to offer assistance in getting into the gunman's iPhone and expedite its response to any legal process, The Verge reported late on Thursday.

The FBI had said that it has been unable to access the encrypted iPhone used by Devin P Kelley, who killed 26 people at a rural Texas church.

"Law enforcement is increasingly not able to get into these phones," Christopher Combs, a special agent at the investigating agency was quoted as saying.

The iPhone Kelley was carrying is said to have crucial information about his activities that led to the shooting.

The FBI and Apple have had strained relations after the December 2015 San Bernardino, California, terror attack when the company had refused the agency's request to help it unlock on the phones of the attacker despite a court order.

In a statement, CEO Tim Cook had said the court order sought and obtained by the FBI would pose a serious threat to data security.